Was ist der richtige Weg, um zwischen Controllern in AngularJS zu kommunizieren?

Question

Wie kommuniziert man richtig zwischen Controllern?

Ich verwende derzeit einen schrecklichen Fudge, der window :

function StockSubgroupCtrl($scope, $http) {
    $scope.subgroups = [];
    $scope.handleSubgroupsLoaded = function(data, status) {
        $scope.subgroups = data;
    }
    $scope.fetch = function(prod_grp) {
        $http.get('/api/stock/groups/' + prod_grp + '/subgroups/').success($scope.handleSubgroupsLoaded);
    }
    window.fetchStockSubgroups = $scope.fetch;
}

function StockGroupCtrl($scope, $http) {
    ...
    $scope.select = function(prod_grp) {
        $scope.selectedGroup = prod_grp;
        window.fetchStockSubgroups(prod_grp);
    }
}