Fediverse

Regarding your question:

Lemmy federation basically works by copying stuff from their source instance to all other federated instances. So if I write a comment on lemm.ee, other federated instances will get their own copy of my comment. They will also all know that the "authority" for this comment is lemm.ee.

If an admin on another instance decides to delete their local copy of my comment on lemm.ee, then they are always free to do so (for example, some instances might want to moderate more strictly), but any actions they take like this are limited to their own instance - for the rest of Lemmy, lemm.ee remains the authority for this comment, so individual remote instance admins taking actions won't have any effect on any other instances.

As for the original topic of modlog federation, basically it just boils down to this: just like with the comment example above, Lemmy instances also save a local copy of incoming federated mod logs. The Lemmy software does not yet have 100% coverage in terms of federating mod logs (for example, there are no federated logs yet for instance admins banning remote users), but this coverage has been increasing, and I expect this will eventually get to 100% (just needs more dev time really).

Also, if some instance admins try to tamper with their mod logs, then other instances can still see the real history, because there is no way for an instance admin to delete copies of their mod log from other instances.