How do I trigger a build when a maven parent project is updated?

I've got a maven parent project that is used by all other maven projects for our team. It specifies things like deployment repositories.

The maven projects that use this parent project aren't having a rebuild triggered when I update the parent project. The parent project is a SNAPSHOT version, so I expected other projects to with the Maven Snapshot Dependencies Trigger to handle this for me.

How do I set things up so that a change to the parent pom triggers a rebuild for all projects that use it?

Cheers,
Peter