This post is older than a year. Consider some information might not be accurate anymore.
The Apache Maven dependency plugin provides the function to remove projects dependencies from the local repository.
The command has to be run in the maven project where the pom.xml resides.
mvn dependency:purge-local-repository -Dmaven.repo.local=/path/to/repo
If you have a lot of snapshot versions, you can remove than completely and download the latest snapshot from your maven repository.