Is there such a thing as a peer to peer database?

I was wondering if  anyone has set up a database system that works sort 
of like a p2p system?
Lets say I want to look for a document that is stored as a blob. If the 
query does not find it on my server it looks at servers in other 
locations for the document. When it finds it puts it in my database as a 
"guest" record. I know that I could do this at the application level but 
wondered if anyone has done such a thing at the server level. Yes I know 
about mirrors and clusters but this is I think just a little different.
Just an idea.