In the case that at the time of generation of a pre-fetch request following a
read request from one of the processors the data stored in other cache devices
cannot be read unless its state tag is changed, a cache controller carries out
weak read operation for causing failure in the pre-fetch request as a fetch protocol.
Alternatively, the cache controller reads pre-fetch data without changing state
tags of other cache devices, sets a weak read state (W), and stores the data. The
data in the weak read state (W) is invalided by synchronization operation of memory
consistency by software. Furthermore, the pre-fetch data is stored in a passive
preservation mode in the present cache device. Even if the pre-fetch data corresponds
to a read request from some other cache device, the preservation of the data is
not informed to the other cache device.
