It's not capable of guaranteeing complete synchronisation of things.

I'm even working on (in my part time) a filter plugin that quickly recognises whether a reply post references a whitelisted identity, by building filters out of posts made by the user - for the purpose of caching first level replies to posts so the relay has it immediately.

I'm going to be using bloom filters to build a recogniser, not sure how the state is going to be stored but probably replaceable private events for the filter itself as a virtual user.