PURPOSE: To decide the time when the cached data are invalidated by the result of the data storing action of another processor.

CONSTITUTION: A server stores plural data value, and a client stores the sub-sets of these data value in a cache. The server processors 10e-10d periodically broadcast the invalidation reports to the client processors 20a-20f. Each invalidation report has the information to identify the date value that is inn a prescribed time set before the processors 10a-10d broadcast the invalidation reports respectively among those data value. Then the processors 20a-20f decide whether the selected data value stored in the cache memories 22 of the processors 20a-20f are updated or not by the processors 10a-10d after those data value are stored in the memories 22 based on the invalidation reports. If the data value are updated, the processors 20a-20f invalidate the selected data value stored in the memories 22.