Deleted the Product image, but still the image exists in the product grid in magento 2

I have deleted the product image using following code

 $imageProcessor = $_objectManager->create('MagentoCatalogModelProductGalleryProcessor');
                $images = $product->getMediaGalleryImages();
                $productGallery = $_objectManager->create('MagentoCatalogModelResourceModelProductGallery');
                foreach($images as $child) {
                    $objectManager = MagentoFrameworkAppObjectManager::getInstance();
                    $productGallery = $objectManager->create('MagentoCatalogModelResourceModelProductGallery');
                    $productGallery->deleteGallery($child['value_id']);
                    $product->setMediaGalleryEntries([]);
                    $imageProcessor->removeImage($product, $child['file']);
                    $product->save();
                }

Image successfully deleted.

But due to the thumbnail image existence, it is still shown in the product grid

Please help how get this thumbnail image and delete

I have tried follwoing way to get thumbnail image, but no luck.

 $productData = $this->productFactory->create();
                $product = $productData->load(1884);
                print_r($product->getThumbnail());