刪除cache文件夾是最好的清空緩存的方式：

- (void)clearAllUIWebViewData {
    // Clear the webview cache...
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
    [self removeApplicationLibraryDirectoryWithDirectory:@"Caches"];
    [self removeApplicationLibraryDirectoryWithDirectory:@"WebKit"];
    // Empty the cookie jar...
    for (NSHTTPCookie *cookie in [[NSHTTPCookieStorage sharedHTTPCookieStorage] cookies]) {
        [[NSHTTPCookieStorage sharedHTTPCookieStorage] deleteCookie:cookie];
    }
    [selfremoveApplicationLibraryDirectoryWithDirectory:@"Cookies"];
}

- (void)removeApplicationLibraryDirectoryWithDirectory:(NSString *)dirName {
    NSString *dir = [[[[NSSearchPathForDirectoriesInDomains(NSApplicationDirectory, NSUserDomainMask, YES) lastObject]stringByDeletingLastPathComponent] stringByAppendingPathComponent:@"Library"] stringByAppendingPathComponent:dirName];
    if ([[NSFileManager defaultManager] fileExistsAtPath:dir]) {
      [[NSFileManager defaultManager] removeItemAtPath:dir error:nil];
    }
}