scons clean would throw an error if there was nothing to do. print a message instead.

SConstruct

@@ -241,6 +241,7 @@ if 'clean' in B.targets:
     do_clean = True
 
 if not quickie and do_clean:
+    if os.path.exists(B.root_build_dir):
         print B.bc.HEADER+'Cleaning...'+B.bc.ENDC
         dirs = os.listdir(B.root_build_dir)
         for dir in dirs:
@@ -248,6 +249,8 @@ if not quickie and do_clean:
                 print "clean dir %s"%(B.root_build_dir+dir)
                 shutil.rmtree(B.root_build_dir+dir)
         print B.bc.OKGREEN+'...done'+B.bc.ENDC
+    else:
+        print B.bc.HEADER+'Already Clean, nothing to do.'+B.bc.ENDC
     Exit()
 
 if not os.path.isdir ( B.root_build_dir):