Today's continuously growing cloud infrastructures provide support for processing ever increasing amounts of scientific data. Cloud resources for computation and storage are spread among globally distributed datacenters. Thus, to leverage the full computation power of the clouds, global data processing across multiple sites has to be fully enabled. However, managing data across geographically distributed datacenters is not trivial as it involves high and variable latencies among sites which come at a high monetary cost. In this paper, the authors propose a uniform data management system for scientific applications running across geographically distributed sites.