We are developing Munin y , a system that allows pro grams written for shared memory multiprocessors to be executed efficiently on distributed memory machines. Thus, Munin overcomes the architectural limitations of shared memory machines, while maintaining their advantages in terms of ease of programming. A unique characteristic of Munin is the mechanism by which the shared memory programming model is translated to the distributed memory hardware. This translation is performed by runtime software, with the aid of semantic hints provided by the user. Each shared data object is supported by a memory coherence mechanism appropriate to the manner in which the object is accessed. This paper focuses on Munin's memory coherence mechanisms, and compares our approach to previous work in this area. This research was supported in part by the National Science Foundationunder Grants CCR8716914 and DCA8619893 and by a National Science Foundation Fellowship. y In Norse mythology, the ravens Munin (Memory) and Hugin (Thought) perched on Odin's shoulder, and each evening they flew across the world to bring Odin knowledge of man's memories and thoughts. Thus, the raven Munin can be considered to have been the first distributed shared memory mechanism.