It sounds like the Forge build could use some validations to ensure the person building the project has an environment that matches the minimum requirements. Obviously, you want as few validations as possible (to make it more portable) but you can work to eliminate them once you know what they are.

http://maven.apache.org/plugins/maven-enforcer-plugin/

Also, newer versions of Maven are suppose to be able to differentiate between origins of dependencies in the local repository, so we should probably be looking closer at the cases when we tell users to clean it out.