1. A method for performing data prefetch in a multiprocessor system, said method comprising: providing each processor within said multiprocessor system with a cache memory, wherein each cache line within said cache memory is formed by a first sub-cache line and a second sub-cache line; issuing a pair of prefetch requests by a requesting processor to its cache memory, wherein one of said prefetch requests is for said first sub-cache line and another one of said prefetch requests is for said second sub-cache line; in response to said pair of prefetch requests miss in said cache memory of said requesting processor, merging said pair of prefetch requests into a combined prefetch request; sending said combined prefetch request to cache memories of all non-requesting processors; and in response to a combined clean response from cache memories of all non-requesting processors, obtaining data for said combined prefetch request from a system memory.