new.js

angular.module('app', [])
  .directive('myAwsomeDirective', function($rootScope) {
    return {
      restrict: 'A',
      link: function(scope) {
        // $scope.$on() returns an unbind function of the binding
        //
        // So use the bind function directly within scope's $destroy event
        // to unbind event automatically.
        scope.$on('$destroy', $rootScope.$on('my:event', function() {
          // your event code here
        }));
      }
    }
  });

old.js

angular.module('app', [])
  .directive('myAwsomeDirective', function($rootScope) {
    return {
      restrict: 'A',
      link: function(scope) {
        // $scope.$on() returns an unbind function of the binding
        var watch = $rootScope.$on('my:event', function() {
          // your event code here
        });
        
        scope.$on('$destroy', watch);
      }
    }
  });