Apple TV 4K adopts old Thread network from iCloud

I am trying to set up a completely fresh Thread network using my Apple TV 4K as the primary Border Router. The reason I need to do this is that I am currently unable to add any new Thread accessories to my existing setup. However, during setup, the Apple TV automatically adopts an old Google Thread network (PAN ID: NEST-PAN-05A8) instead of creating a new one.

I have already tried the following troubleshooting steps:

• Unplugged all other Thread Border Routers in my home (Google Nest Hubs, Homey Pro).
• Deleted my Home in the Apple Home app.
• Factory reset the Apple TV 4K.
• Set up the Apple TV using a completely new Apple ID as a test. When doing this, it successfully created a brand new Thread network, and I was immediately able to add accessories without any issues. This confirms the issue is tied to the data synced to my primary iCloud account.

It appears my primary iPhone/iCloud Keychain is holding onto the old Thread credentials (likely via Thread Credential Sharing) and automatically pushes them to the Apple TV during the setup process, even when the Google devices are powered off.

How can I completely purge these cached Thread network credentials from iOS/iCloud so that my Apple TV is forced to generate a brand new Thread network on my main account?