Over the past years grid infrastructures have been deployed at larger and larger scales, with envisioned deployments incorporating tens of thousands of resources. Therefore, application scheduling algorithms can become unscalable (albeit polynomial) and thus unusable in large-scale environments. One reason for unscalability is that these algorithms perform implicit resource selection. One can achieve better scalability by performing explicit resource selection independently from scheduling in a "decoupled" approach. Furthermore, we hypothesize that one can achieve similar or even better performance as with the non-decoupled approach, which we call the "one step" approach, by selecting resources judiciously. Leveraging the Virtual Grid abstraction, we demonstrate that the decoupled approach is indeed both scalable and effective in large-scale and highly heterogeneous resource environments.