Target domain is not available in RUM from the drop down menu (4348998)

Stand-alone separate ADAM instance has been created and now when using RUM there are no domains to select, the menu is blank.
How can this field be populated again?
Typing each domain name manually is not desired since it is a big environment and when typing mistakes can be made.

When migrating computers:
In RUM in the upper task bar click on "Refresh Computer List" icon or use the steps Actions - "Refresh Computer List" (it might take some time to complete, don't interrupt) and this should populate the RUM DB with all available domains.

When processing computers:
Perform the same step as mentioned above and then in RUM under filters ensure you have selected all involved domains.
RUM will display domains under filter options only if at least one computer for a particular domain  was added in RUM (at least once).
To re-phrase: If you have added a computer from domain A, B and C then only domains A, B and C will be visible under filter options.