Recently distributed shared memory (DSM) systems have received much attention because such an abstraction simplifies programming. An important class of DSM implementations is one which uses cache memories to improve efficiency. In this paper, we present a cache-consistency protocol which uses considerably less communication as compared to previously proposed protocols. This is realized by maintaining state information and capturing causal relations among read and write operations. We prove that the protocol satisfies a formulation of sequential consistency. We also present several modifications to the protocol and compare the classes of execution histories captured by these protocols and several previously.proposed protocols.