I had a second scenario this week that gave me pause before resulting in the above practice.

ProductA is developed and maintained by ScrumTeamA, who writes automated checks for all User Stories and runs the checks in a CI.  ProductB is developed and maintained by ScrumTeamB.

ScrumTeamB developed UserStoryB, which required new code for both ProductA and ProductB.  ScrumTeamB merged the new product code into ProductA…but did NOT merge new test code to ProductA.  Now we have a problem.  Do you see it?

When ProductA deploys, how can we be sure the dependencies for UserStoyB are included?  All new product code for ProductA should probably be accompanied with new test code, regardless of the Scrum Team making the change.

The same practice might be suggested in environments without automation.  In other words, ScrumTeamB should probably give manual test scripts, lists, test fragments, or do knowledge transfer such that manual testers responsible for ProductA (i.e., ScrumTeamA) can perform the testing for UserStoryB prior to ProductA deployments.