fix(clearCache): ensure async transition completed

Closes #2939

Author: adamdbradley

Diff for: js/angular/service/history.js

@@ -615,8 +615,10 @@ function($rootScope, $state, $location, $window, $timeout, $ionicViewSwitcher, $
      * This both removes the view element from the DOM, and destroy it's scope.
      */
     clearCache: function() {
-      $ionicNavViewDelegate._instances.forEach(function(instance) {
-        instance.clearCache();
+      $timeout(function() {
+        $ionicNavViewDelegate._instances.forEach(function(instance) {
+          instance.clearCache();
+        });
       });
     },