A Wikipedia:Cache is the poor computer scientist's trick to have something available at any time without having to fetch it again. This works in a lot of situations, but in many it remains the poor solution compared to having been pushed that something as it changes. Of course you can still call it a cache, but in fact you are holding a legitimate mirror or view of something, if that something will make sure you always have the current version, not some old cached copy.
PSYC is oriented towards solving problems by push. The decentralized state is a mechanism which lets you keep information in sync over a whole network of subscribers. We don't use the word cache here. It has too much negative connotation.
The Wikipedia:Web cache article hits the nail more precisely. In order to maintain a cache of web documents, web applications first use an HTTP If-Modified-Since GET request to ensure it being up-to-date before showing it to the user. This introduces a latency in displaying web pages. You can feel it when you hit the back button several times in your web browser. Ironically, the HTTP specification actually forbids web browsers from changing history by refreshing pages you already saw - but most web browsers ignore that.
In a perfect PSYC constellation, you should be able to watch a person's profile using PsycZilla, and, given you are subscribed to her, whenever that person changes some data in its profile, you would be seeing it refresh on your screen in realtime.