With the exponential growth of hosts and tra c workloads on the Internet, collaborative web caching has been recognized as an e cient solution to alleviate web page server bottlenecks and reduce tra c. However, cache discovery, i.e., locating where a page is cached, is a challenging problem, especially in the fast growing World Wide Web environment, where the number of participating proxies can be very large. In this paper, we propose a new scheme which employs proxy a nities to maintain a

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... ic distributed collaborative caching infrastructure. Web pages are partitioned into clusters according to proxy reference patterns. All proxies which frequently access some page(s) in the same web page cluster form an \information group". When web pages belonging to a web page cluster are deleted from or added into a proxy's cache, only proxies in the associated information group are noti ed. This scheme can be shown to greatly reduce the number of messages and other overhead on individual proxies while maintaining a high cache hit rate. Finally, we employ trace driven simulation to evaluate our web caching scheme using three web access trace logs to verify that our caching structure can provide signicant bene ts on real workloads.