Recently, scalable multiprocessor systems are actively developed for general-purpose computing, which are based on distributed shared memory (DSM) architecture to boost up both programmability and scalability. In this paper, we survey and analyze cache coherence protocols in non-uniform memory access (NUMA) multiprocessor systems. In particular, it has been easily inferred that specialized hardware suitable for NUMA multiprocessor systems with commodity symmetric multiprocessors (SMPs) is highly required. The cache coherence protocol combined with specialized hardware can significantly improve the performance and scalability of NUMA multiprocessor systems, providing better programmability.