Looking for help cleaning up legacy Thread networks

[boreal fable]

A little background: I own a SkyConnect that I originally ran in multipan mode, but I had reliability issues with it, so I switched it to full Zigbee. I also have a Google Nest Hub v2 with Thread Border Router functionality, but it’s still stuck on Thread 1.3. Because of that, I bought a new ZBT‑2 device.

I only have two Thread end devices, so I’m fine wiping everything Thread and Matter related to start fresh. Now that the market is starting to get a decent selection of Matter devices, I want to rebuild cleanly. I received the ZBT‑2 last week and want it to host my primary Thread network and act as the Border Router for Home Assistant.

After several partially successful setup attempts, I finally have HA showing what looks correct: One Thread network (“home‑assistant”) with a single Border Router - the HA OpenThread Border Router using the ZBT‑2.

The old Thread network created by my Nest Hub still seems to be cached somewhere. Even after wiping everything, HA still tries (and fails) to join new Thread devices to the old “NEST‑PAN‑xxxx” network, which no longer exists because the Nest Hub is unplugged.

I attempted a full purge:

• Removed OpenThread Border Router, Thread, ZBT‑2, and Matter from HA Integrations
• Deleted the Nest Hub and both Thread devices from HA Devices
• Disabled and/or deleted anything else related to Thread or Matter
• Removed the Nest Hub from the Google Home app
• Unplugged the Nest Hub
• Uninstalled both Google Home and the HA Companion app from my phone
• Rebooted HA multiple times
• Rebooted my phone
• Reinstalled only what was needed—no Google apps or devices added back
  Despite all this, HA still tries to join devices to the old “NEST‑PAN‑xxxx” network.

Question
Where else might that network information be stored, and how can I remove it completely?

[onyx sierra]

Is this information not stored in the Google Play services or something? For Android at least and for iOS in the Keychain?

[boreal fable]

I saw some message in my troubleshooting that led me to believe that the problem is, as you pointed out, on my Android phone (It's A Google Pixel 9 Pro). Google's only current way of solving this I can find is to clear the entire Google Play Services cache (to the tune of 1.47GB ???) and reboot. That apparently cleared out a lot of other stuff too. I have spent the last 2 hours trying to get my phone functioning properly since then. Currently it seems that matter no longer exists on my phone - according to everything I can find on the device. Trying to add devices via the companion App also tells me that Matter is currently unavailable. So hopefully I have cleared out the stored Network info, but I have no way of knowing because now the phone no longer "speaks" Matter.

Google's advice is to apply helpdesk fix #2: Just wait longer
PLUS
Helpdesk fix #1: Daily reboots, and that should take care of it eventually.
Thanks Google...

I do appreciate the response - it helps validate that I am hopefully going down the right track.

Cheers,
Fred

[boreal fable]

SUCCESS!
After clearing out the cache there were a few steps that needed to be followed:
Step 1 - I needed to download and install 800mb worth of patches (the phone was listed as up to date this morning - I don't think it's a coincidence), and reboot.
Step 2 - I needed to re-install the Google Home app which re-initialized Matter
Step 3 - I had to manually re-apply permissions to the HA Companion app that got revoked when clearing the cache.
Step 4 - Final reboot for the phone for all changes to apply niceley.

Matter devices are now being added to Home Assistant under the correct Thread network.
Hope this info helps someone else out in the future.

Thanks @onyx sierra for the good advice!