From a technical point, blocking would only be obvious to the blocker. The server would remember your settings and not show you anything related to the person you blocked.

The blocked being unable to see you would require a lot more technical work. Easy if you are both on the same server as the server could register the block. If they blocked is on a different server then both servers would have to accept the block registration. And then another server needs to spend resources making sure that their blocked user gets content filtered out that contains your name from seeing them.