1. A method of designating a least recently used entry in a content addressable memory which holds data values having respective resource identifiers comprising: storing a plurality of the resource identifiers in entries of the content addressable memory with respective count values indicating a time sequence in which the resource identifiers were stored; changing selected count values to higher count values in response to access requests for corresponding resource identifiers; after each access request, searching the content addressable memory to find one of the entries having a lowest count value, and writing the resource identifier of the entry having the lowest count value to a least recently used register; receiving a request to store a new resource identifier in the content addressable memory; determining that the new resource identifier is not currently stored in the content addressable memory and that the content addressable memory has no currently unused entries; reading the least recently used register to identify the resource identifier therein as a least recently used resource identifier; and allocating the entry corresponding to the least recently used resource identifier for storing the new resource identifier.