In this paper, we study the impact of tasks reallocation onto a multi-cluster environment where clusters are heterogeneous and use different resources management policies. In this context, we propose a reallocation mechanism that migrates waiting jobs from one cluster to another. We performed simulations using real traces to study benefits of reallocations. We compared two algorithms providing the reallocation mechanism, each with several heuristics to schedule jobs. Results show that in some cases it is possible to obtain a substantial gain on the average job response time (more than a factor of two). In the other cases, the reallocation mechanism is beneficial most of the time, making of great interest the implementation of a reallocation mechanism in a Grid framework.