How to optimize process in php or run it in the background?

I have a file in php that is responsible for closing the session but before it must change the status in several different databases, this process takes a bit, so the browser stays waiting and until it ends redirects to index .php This is the code to close the session ...

      <?php
      include 'HistorialController.php';
      include_once 'clases/Sistemas.php';
      session_start();

      $_SESSION['login'] = false;
      $_SESSION['recordar'] = 'no';         

      $liberar = new Sistemas('');
      $liberar->libera();

      unset($_SESSION['login']);
      header('Location: index.php');    
      ?>

The release code is the following ...

       /**
       * Metodo que Libera las imagenes ocupadas por el usuario al salir de la session
       **/
       public function libera(){
           $id_user = $_SESSION['id_usuario'];
           $actualiza = "UPDATE Imagen SET estatuspm_web=0 WHERE id_usuariopm_web=" . $id_user." and estatuspm_web=1";
           for ($i = 0; $i < count($this->listaSistemas); $i++){ //RECORRIDO DE LOS SISTEMAS 
                $sistemaActual = $this->listaSistemas[$i];                 
                $baseConn = new BaseConexion("Sistema_".$sistemaActual); 
                if ($conn = $baseConn->conectar()) {
                     sqlsrv_query( $conn, $actualiza, $params);                      
                }
                $baseConn->close();
            }
       }