The organization of caches into a hierarchy of levels. A typical two-level cache used for dispensing Web pages might have local caches associated with a cluster of computers connected via a local area network and a regional cache which serves all the computers in all these networks. If a browser resident on the local network asks for a Web page which is not in the local cache for its network, then the regional cache is consulted. If the page requested is found there, it is returned via the local cache to the browser that asked for it. If it is not found, it is retrieved from the server on which it resides. See also caching, caching policy and caching proxy server.