Caching at the proxy server is in use throughout the world to reduce the network congestion and access latency on the WWW. To gain the maximum benefits of caching, the sharing of the Web caches among proxy servers has recently become an important issue. The sharing scheme is generally performed by the Internet Cache Protocol (ICP), which supports the discovery of Web objects from neighboring proxy caches. However, the sharing scheme via ICP has two fatal weaknesses: 1) message multicast overhead and 2) redundant caching of same objects among collaborative proxies. In this paper, we present a new Web cache sharing scheme. Our new scheme reduces the message overhead of ICP dramatically. It also reduces the duplicated copies of the same objects in globally shared Web caches. Using trace-driven simulation, we show that the proposed scheme outperforms ICP and Cache Array Routing Protocol (CARP) in terms of various performance measures.