Magazine bans not federating with lemmy.world (and potentially others)

I've just discovered that lemmy.world (and potentially other) users I've banned from my magazine are still able to comment, comments I can't see on kbin but that do show up on lemmy.world.
(E: I already knew removed comments still show up on other instances, but assumed that sorts itself out in time, but now I'm not so sure)

This makes modding futile.

I want to make sure my space is safe and not hostile to those of us who already deal with bullshit everywhere else, and I can't do that when this is the case.

How do we fix this?