How is "No relaying of other user's searches" possible in a decentralized network ?

A method I can think of is if the shared files index that each user has is encoded into a bitcoin style index that can be accessed using the dht mechanism to look up a specific string or hash value and retreive the encoded data from a global user based cache, a shared index would require space at each node and some method of storing redundant duplicate data in case a specific location is down but "share"  /"perfect dark" use something similar to cache files and so its not unheard of, its a good question however.