Laravel5.2 Session use forget() but no work

I use Laravel5.2 to build a E-commerce platform and get some troubles.When I loginout user state and I use Session::forget('user') or $request->session()->forget('user'), it works in current page,and I redirect to the login page and dd(Session::all()) find the session 'user' still exist!!! so I am confused to know what is wrong with it? plz tell me the reason,thanks all.

ps. loginout code

public function logout(Request $request)
{
    if ($request->session()->has('user')) {
        $is_forgotten = $request->session()->forget('user');
        if ($is_forgotten === null)
            echo json_encode(['result' => 1]);
        exit;
    }
    echo json_encode(['result'=>0,'msg'=>'loginout error']);
    exit;
}