The solution to referencing across workspaces is to build a Smart List in the target workspace, share the Smart List to the destination workspace, and then reference that Smart List for cross marketing.
For example, let's say that there is particular program membership that you want to access in another workspace. In that workspace, create a Smart List within a folder, and then share that folder to the destination workspace. Sharing the Smart List will allow the List to be targeted within the cross marketing campaign.
Who This Solution Applies To
Instances with workspaces