Most large-scale scientific workflows take place in multiple collaborative datacenters for access to community-wide resources, while adhering to each datacenter's non-uniform resource limits. However, moving both initial input datasets with predetermined locations and intermediate datasets needing placement decisions across geo-distributed datacenters hinders efficient execution of large-scale data-intensive scientific workflows. Thus, scientific workflow's data and task co-scheduling deal with situations such as pre-placed initial input datasets, placement of intermediate datasets and each datacenter's non-uniform computation and storage constraint, while minimizing the cross-datacenter data transfer. Since this scheduling problem is known to be NP-hard, here, we propose a novel approach, based on the multilevel graph coarsening and uncoarsening framework, together with a specialized hybrid genetic algorithm having distinctive graph partition driven features of repair and local improvement, for scheduling data-intensive scientific workflows in geo-distributed datacenters and optimizing the cross-datacenter data transfer volume. Extensive simulations, based on four real-world workflow traces, show that our algorithm significantly reduces the overall geo-distributed data transfer and demonstrate its effectiveness.