This paper proposes using shared memory for caching latency sensitive distributed data structures on Symmetric Multi-Processor nodes of clusters connected with commodity networks. Shared memory mirroring is a hybrid approach that replicates data across cluster nodes and distributes data within each node. The user is responsible for managing consistency of the data cached within the mirrored data structures. The method is shown to be very effective in improving the performance of a real scientific application on clusters equipped with Ethernet, Myrinet, or Quadrics networks.