We are into migrating different domains to only one domain, we have users in many different domains but now we have created on central domain and users from all these domains are added to one central domain, we have around 300-400 site collections, what we want to do is - 1. Select one user from this central domain, find similar user in other domains 2. Replace the old domain id in all site collections with new central domain id. 3. Repeat this for all other users. Kindly help us, urgent help will be highly appreciated.