How to clear Http cookies in angularness?

HI i am using the below method to call a web service from my login page.

var url='url.com'+Username;
      $http.defaults.headers.common['Authorization'] = 'Basic ' + Base64.encode(Username + ':' + password);
      console.log($http.defaults);
      $http({method: 'GET', url: url,headers: { 'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8','Authorization':'Basic ' + Base64.encode(Username + ':' + password)}}).

          success(function(data) {
              if(data=='' || data==null || data=='undefined'){
                  var alertPopup = $ionicPopup.alert({
                      title: 'Info!',
                      template: 'Invalid Password, or no user found with this Email Address'
                  });
                  alertPopup.then(function(res) {
                      console.log('Invalid Password, or no user found with this Email Address ');
                  });

              }
              else{

                  //console.log("LOGIvar: " + data+ " - PW: " + password);
                  console.log(JSON.stringify(data));
                  $state.go('app.tasklists');
              }


              // this callback will be called asynchronously
              // when the response is available

          }).

it working properly. in logout method i deleting the http cookies like

$http.defaults.headers.common['Authorization']='clear';

after that if i enter a wrong password or enter another user i am getting the previously logged i user. is there i am doing any wrong?