You can separate stories by workspaces and these workspaces are completely isolated.
One or several members can be assigned to specific workspaces and admins can manage their access. There are no restrictions based on domains.
Create Workspace
1) Access all workspaces from the left sidebar,
2) Create one by clicking on "New workspace" on the top right.
Edit Workspace
1) Access all workspaces from the left sidebar,
2) Edit one by clicking on "pencil" icon