static Set<File> garbageCollectProgramJars() {
  Set<S> names = map fileName(programJarsLoadedInAllVMs());
  for (File f : filesInDirs(javaxCachesDir(#1002203), javaxCachesDir(#1001638)))
    if (hasExtension(f, ".jar") && !names.contains(fileName(f)))
      deleteFileVerbose(f);
}