Cost-effective cooperation among a network of edge caches is widely accepted as an effective mechanism for enhancing the scalability, performance, and reliability of edge cache networks. However, the problem of how to form cache groups for achieving effective and efficient cooperation in edge cache networks has largely been unexplored. In this paper, we identify two important factors that need to be considered while forming cooperative groups, namely, network proximities of edge caches and network distances of the caches to the origin server. We propose two novel cache clustering schemes for accurately partitioning the caches of a given edge cache network into specified number of cache groups. The first scheme, called the Selective Landmarks scheme (SL scheme), accurately partitions the edge cache network into cooperative groups based on the network proximities of the caches. The second cache group formation scheme, called Server Distance sensitive Selective Landmarks scheme (SDSL scheme), provides a careful combination network proximities and server distances. Our experiments indicate that the proposed techniques can yield significant performance benefits.