The cache invalidation patterns of several parallel applications are analyzed. The results are based on multiprocessor simulations with 8, 16, and 32 processors. To provide deeper insight into the observed invalidation behavior the invalidations observed in the simulations are linked to the high-level objects causing them in the programs. To predict what the invalidation patterns would look like beyond 32 processors, a classification scheme for data objects found in parallel programs is proposed. The classification scheme provides a powerful conceptual tool to reason about the invalidation patterns of parallel applications. Results indicate that it should be possible to scale well-written parallel programs to a large number of processors without an explosion in invalidation traffic. At the same time, the invalidation patterns are such that directory-based schemes with just a few pointers per entry can be very effective. The variations in invalidation behavior with different cache line sizes are discussed. The results indicate that cache line sizes in the 32-byte range yield the lowest data and invalidation traffic. >