Each 8400 is connected to two SAN switches. Let's call them "Fabric A" and "Fabric B". Since you have two sites, you have two "Fabric A" switches and two "Fabric B" switches. The two "Fabric A" switches join to become a singlesite-spanning "Fabric A", and the two "Fabric B" switches join to become a single site-spanning "Fabric B".
There is NO connection between the "Fabric A" switches and the "Fabric B" switches.
Zoning is a fabric function. You do your PWWN zoning twice; once on one of the "Fabric A" switches and once on one of the "Fabric B" switches.
Read the HPE SAN Design Reference Guide(aka "SAN Design Guide") at https://h20272.www2.hpe.com/SPOCK/Pages/spock2Html.aspx?htmlFile=dg_san_design.html