Clear NGINX page cache when WooCommerce product inventory levels are changed (only tested on GridPane with Redis page caching enabled)

clear_cache_when_stock_changes.php

//clear entire cache when stock is reduced or replenished

function clear_cache_when_stock_changes( $order ) {
	if(class_exists('PhpRedis_Purger') || class_exists('Predis_Purger')){
		global $nginx_purger;
		$nginx_purger->purge_all();	
	}
}
         
add_action( 'woocommerce_reduce_order_stock', 'clear_cache_when_stock_changes', 10, 1 );
add_action( 'woocommerce_restore_order_stock', 'clear_cache_when_stock_changes', 10, 1 );

clear_product_page_caches_when_stock_changes.php

//only clear product page caches when stock changes

function clear_product_page_caches_when_stock_changes( $order ) {

	if(class_exists('PhpRedis_Purger') || class_exists('Predis_Purger')){
		if($order){
			global $nginx_purger;

			foreach ( $order->get_items() as $item_id => $item ) {
				$product_id = $item->get_product_id();
				$nginx_purger->purge_post( $product_id );
			}
		}
	}
}

add_action( 'woocommerce_reduce_order_stock', 'clear_product_page_caches_when_stock_changes', 10, 1 );
add_action( 'woocommerce_restore_order_stock', 'clear_product_page_caches_when_stock_changes', 10, 1 );

Ya this hasn't been tested rigorously, but that was actually something I originally had in there and accidentally deleted when troubleshooting. There are a few ways to check for presence of the active plugin. I prefer to look at classes and have added that back in, but you can also check this with is_plugin_active()