Research on future 5G networks has geared up in the past couple of years, and among many other, seamless mobility is considered as a cornerstone of 5G networks. Lately, many mobility solutions have been put forward, among them are Software Defined Networking (SDN) based Proxy Mobile IPv6 (PMIPv6) and Distributed Mobility Management (DMM). SDN-PMIP advocates the benefits of control and data plane separation, but poses major limitation in terms of mobility support across multiple domains. DMM takes care of inter-domain handovers through on demand mobility feature, but has limitations like excessive control signaling, tunneling overheads and inefficient routing. This paper presents a comprehensive solution to provide mobility across multiple domains in SDN-PMIP by utilizing the on demand mobility feature of DMM. Concept of on demand mobility is to provide mobility support to only those mobile nodes which require it, by exploiting the IPv6 mandatory feature of supporting multiple prefixes. In our proposed solution, controllers in multiple SDN-PMIP domains communicate with each other in distributed manner to facilitate seamless inter-domain mobility. The proposed solution also introduces a new optimized routing concept which resolves the triangular routing issue faced by various inter-domain mobility solutions. Analytical modeling based performance evaluation in terms of handover delay, transmission delay and tunnel usage, shows that the proposed solution achieves substantial improvements over previous works.