[scope] What's the correct way to communicate between controllers in AngularJS?

Using get and set methods within a service you can passing messages between controllers very easily.

var myApp = angular.module("myApp",[]);

myApp.factory('myFactoryService',function(){


    var data="";

    return{
        setData:function(str){
            data = str;
        },

        getData:function(){
            return data;
        }
    }


})


myApp.controller('FirstController',function($scope,myFactoryService){
    myFactoryService.setData("Im am set in first controller");
});



myApp.controller('SecondController',function($scope,myFactoryService){
    $scope.rslt = myFactoryService.getData();
});

in HTML HTML you can check like this

<div ng-controller='FirstController'>  
</div>

<div ng-controller='SecondController'>
    {{rslt}}
</div>