How best to trigger builds with multiple repositories?

Trying to create a pipeline which works with multiple SCM repositories, which produce interdependent applications that need to be deployed together, I’d like Jenkins to poll each of the repositories and execute a pipeline when changes are pushed to any of the repositories.

I’ve attempted this by adding a Pipeline job,
In the Build Triggers section selecting Poll SCM.
In the Pipeline section selecting Pipeline script from SCM then adding each of the repositories referenced in the pipeline I want executed.

It seems like each repository added requires its own jenkinsfile

What does Jenkins do with the Jenkinsfiles from each of the repositories added?

It doesn’t seem to be executing all of them, it seems only one is executed, what’s the logic used to select the jenkinsfile which gets executed?