The classpath container supports a Resolve task on its context menu, but not a CleanCache. This is unfortunate, because, if the resolve fails to locate some artifacts (say, because of an intermittent DNS failure or web server outage), it records ".notfound" entries in the cache, making future Resolves continue to fail.
The only solution I've found is to create an ant build.xml with a cleancache target, and run that in these situations. It would be preferable if I could clean the cache directly from the classpath container context menu. Since the ivy:cleancache task already exists, this would hopefully involve changing mostly UI code.