A grid system is a dynamic and distributed environment which contains numerous entities and resources, and is involved in large-scale processing and resource sharing. One of the critical issues is to assure a high level of security among all interacting clusters and their nodes in such a dynamic environment. The proposed model presents a coherent trust computation framework for quantifying and qualifying the trustworthiness of entities in different clusters. This model considers that at a particular context of time a grid node can belong to one cluster. The objective is to provide a trust management system that can compute, maintain and update consistent trust information for the entities in a cluster grid.