A multiprocessor system has a background memory and a plurality of processing elements, each comprising a processor core and a cache circuit. The processor cores execute programs of instructions and the cache circuits cache background memory data accessed by the programs. A write back monitor circuit is used to buffer write addresses used for writing data by at least part of the processor cores. The programs contain commands to read the buffered write back addresses from the write back monitor circuit and commands from the programs to invalidate cached data for the write back addresses read by the commands to read the buffered write back addresses. Thus cache management is performed partly by hardware and partly by the program that uses the cache. The processing core may be a VLIW core, in which case instruction slots that are not used by the program can be made useful to include instructions for cache management.