ARC使用完成处理程序保留循环

Question

如何在以下代码中修复ARC保留周期？

-(void) processRequest:delegate:(id<Delegate>)delegate {

__block  Request * request;
request = [[Request alloc] completionHandler:^(Response * response){

    [delegate removeCachedRequest:request];

    if (completionHandler)
    {
        completionHandler(response);
    }

}];

}