It would be useful if there were a way to manually force dependencies to be re-retrieved. Some examples of this are:

• -SNAPSHOT
• uri(git://...)

Others might fall into this bucket too, though I haven't tried them myself:

• Ivy dependencies with a + in their revision
• file(...)
• Other types of uri(...)

Here are some threads about where the community has run into this:

• http://stackoverflow.com/questions/8864317
• http://groups.google.com/group/simple-build-tool/browse_thread/thread/7ca098521557062c
• http://groups.google.com/group/simple-build-tool/browse_thread/thread/5b59604bb08114b3