How to add a custom domain in different project areas of Design Management (like other System defined domains)
Accepted answer
Being in Domains project click configuration context menu item (close to the upper right corner, should be called "Domains"), find submenu "Create" and "Snapshot".
Click "Snapshot" menu item and follow to the wizard's instructions.
Once snapshot is created, you should see your design domain in the domain association dialog.
Regards,
Andrey