How to remove my instance users from other instances

cross-posted from: random-hero.com/post/51002

Hello everyone! Recently I have removed a couple of bot users from my Lemmy instance via DB query (I removed them from person table). Those bots were subscribing to hundreds of communities on other instances which I don’t really want to spend resources on fetching new posts and updates.

I have purged those communities from my instance but they keep reappearing. As far as I can tell, this happens because other instances still “think” that users from my instance (bots, which don’t exist already) are still subscribed, and therefore send updates to my instance.

How can I completely get rid of those communities?