In your case yes. Since both your PSCs are separate SSO domains, the easiest solution without rebuilding would be to point one of your vCenters to the same PSC as the other vCenter. See instructions.
How to repoint vCenter Server 6.x between External PSC within a site (2113917) | VMware KB
Technically, after you do this, you could get rid of the unused PSC and redeploy it. This time joining it to the same SSO domain as the first PSC. Now you would have two PSCs on the same SSO domain and you could go through the repoint process again to move vCenter back to the PSC in the same site.