In a computer system with a plurality of levels of cache storage, a cache control method prevents data duplication among the levels of cache storage to increase cache storage utilization. A high-level cache staging unit stages reads data from a disk unit, stages the data to a high-level cache, and instructs to destage the data, which has been read, from a low-level cache. A high-level cache destaging unit writes data to be destaged to the disk unit, instructs to stage the data, which has been written, to the low-level cache, and destages the data from the high-level cache. A low-level cache staging unit stages a data, which is written by the high-level cache destaging unit, to the low-level cache. A low-level cache destaging unit destages a data, which is instructed by the high-level cache staging unit, from the low-level cache.