How does this work? I thought only users can block specific communities. My account is on Lemmy.world, but if I'm reading community on lemmy.dbzer0.com, that stuff is stored their server, so why does lemmy.world lock me out of reading it?
You are not reading content from lemmy.dbzer0.com unless you specifically have only that at the beginning of the address. If you have lemmy.world instead, it means you are trying to view content cached there, which no longer exists.