Communication Limits probably your best bet.
I assume here you mean that each Workspace has a corresponding Lead Partition?
Continuing what Josh said, leads don't exist in workspaces. Workspaces have access to lead partitions. Leads sit in lead partitions. You can give workspaces access to multiple lead partitions. A lead can only reside in a single lead partition (as well as the default partition, which contains all leads). If you have some sort of purposeful duplicate process, you can hide a lead partition from all but one workspace (including the default workspace) and have it contained in that partition as well as a duplicate in another partition. So I guess before we can provide the best answer, is this a single lead that exists in a dedicated lead partition, where multiple workspaces have access to it?