As the rapid growth of renewable energy sources (RESs) with fluctuating and uncertain power generation, reserve shortages become increasingly severe, limiting the further integration of RESs and making it essential to exploit additional reserve sources. The fast-growing data centers offer significant potential to provide reserves due to their spatial and temporal dispatch flexibility. However, large quantities of jobs in the data centers have different computing requirements, making it challenging to estimate the availability of data centers for providing reserves. Meanwhile, the regional resource mix leads to uneven reserve distribution and mismatches between reserve supply and demand. The cross-region reserve supply has the capability to mitigate such mismatches as it allows different regions to provide reserve to each other. This paper enriches the reserve sources in multi-region system dispatch to enhance renewable energy integration by exploiting the reserve supply capabilities of data centers and cross-region systems. The model for available reserves of data centers is proposed via analyzing the envelope of computing constraints of aggregated jobs. In addition, a comprehensive cross-region reserve supply model is presented by considering reserve supply and demand limitations and reserve transmission capability. Case studies are performed and the results show that the data centers can provide a substantial amount of reserves. Both the migration of jobs among data centers and the cross-region reserve supply transfer reserve resources among multiple regions. Simulations on a real-world power grid system further demonstrate that unlocking the reserve supply potential of data centers can reduce operating costs by 0.4% and the curtailment of RESs by 1.7%.