Your best bet to do this would be to add a filter/hook on the specific tag. See this snippet at the WooCommerce API docs site on excluding a category for the proper format and to get going in the right direction. http://wcdocs.woothemes.com/snippets/exclude-a-category-from-the-shop-page/
But if you want a down and dirty way to filter for a specific tag on this content part then you can wrap an if then around your woocommerce_get_template_part().
<?php while ( have_posts() ) : the_post(); ?>
<?php if ( *** product has tag *** ) { ?>
<?php woocommerce_get_template_part( 'content', 'product'); ?>
<?php endif; ?>
<?php endwhile; // end of the loop. ?>
You can look at the API docs on the product tags at http://wcdocs.woothemes.com/apidocs/class-WC_Product.html#_get_tags
Make sure you’re following WooCommerce theme customization recommendations at http://wcdocs.woothemes.com/codex/template-structure/
Unless you want this to be global you’ll have to account for the various outputs and determine when you don’t want to filter both products and tags.