Manage ng-if from another controller - angularjs

Question

I have prepared a Plunkr that provides the code:
https://plnkr.co/edit/WXtQxVcdgyvnaajbs4eJ?p=preview
I have assigned the object $scope.menu.show in controller toolbarCtrl that controls whether the menu is created or not.
<md-menu id="menu" ng-controller="toolbarCtrl" ng-if="true"> ...
When toolbarCtrl gets initialized I can control whether the menu is shown but I would like to control it from another controller. In this case I created two buttons in mainCtrl that produce true or false and I'm trying to assign the value to the $rootScope but that doesn't work.
How can I do that?
UPDATE:
Although jtmingus solution works perfectly I came up with another solution that doesn't need events.
I created this factory service:
app.factory('menuState', function () {
var state = {val: false};
function getState() {
return state;
}
function setState(newState) {
state.val = newState;
}
return {
getState: getState,
setState: setState
}
});
Then at the toolbarCtrl controller I initially hide the menu
app.controller('toolbarCtrl', function($scope, menuState) {
// hide the menu
menuState.setState(false);
// pass the value to the menu
$scope.state = menuState.getState();
});
on the mainCtrl I define the button clicks like that:
app.controller('mainCtrl', function($scope, $rootScope, menuState) {
$scope.state = menuState.setState;
});
and 2 buttons on the the main.html
<md-button class="md-primary md-raised" ng-click="setState(true)">Show</md-button>
<md-button class="md-primary md-raised" ng-click="setState(false)">Hide</md-button>

Answer 1

The way that data generally should be shared through controllers is by using a service. Because you need both controllers to watch the same state, you can use Angular's events, specifically the $on event.
Here is an article that will walk you through having multiple controllers watch the same state:
https://variadic.me/posts/2013-10-15-share-state-between-controllers-in-angularjs.html
Edit: After looking through this article some more, I realized it's not the best explanation, and there are some things in the code that don't work. For example, if you try to pass arguments in with a $broadcast call, the $on function needs two paramaters–event and args.

Answer 2

On the controller from which you want to initiate showing the menu,
app
.controller('MainCtrl', ['$scope', function($scope) {
$scope.$broadcast('menu:show');
}])
.controller('ToolbarCtrl', ['$scope', function($scope) {
var ToolbarCtrl = this;
$scope.$on('menu:show', function() {
ToolbarCtrl.showMenu = true;
});
}])
In the markup switch using this value
<md-menu id="menu" ng-controller="ToolbarCtrl" ng-if="ToolbarCtrl.showMenu"> ...