This paper presents a new receiver-initiated multicast algorithm called Robber for distributing large amounts of data from one cluster to multiple other clusters in grid computing environments. Robber is inspired by BitTorrent but is designed specifically for cluster grids. It uses a cooperative approach where nodes in the same cluster work together to efficiently retrieve data from peer clusters. Unlike static load balancing approaches, Robber dynamically adapts the workload of each node based on its relative performance within a cooperative. This avoids slower nodes from degrading overall throughput. The paper evaluates Robber experimentally and shows it outperforms BitTorrent and an earlier static load balancing approach, achieving throughput competitive with ideal multicast when bandwidth is stable and adapting better when bandwidth changes.