Today’s Grids, Peer-to-Peer infrastructures or any large computing collaborations are managed as individual virtual domains (VDs) that focus on their specific problems. However, the research world is starting to shift towards world-wide collaborations and much bigger problems. For this trend to realize, the already existing collection of many resources and services needs to be shared across owning VDs in secure and efficient ways, and at the least administrative costs. In this paper we identify the requirements for and propose a specific solution based on usage service level agreements (uSLAs) for this problem of VD sharing. Further, we propose an integrated architecture that provides uSLA-based access to resources, supports the recurrent delegation of usage rights, and provides faulttolerant resource co-allocation.