Magento2- How Magento cache clearing works with Varnish

According to Varnish documentation, “A purge is what happens when you pick out an object from the cache and discard it along with its variants.” A Varnish purge is very similar to a Magento cache clean command (or clicking Flush Magento Cache in the Magento Admin).

In fact, as discussed in this section, when you clean, flush, or refresh the Magento cache, Varnish purges as well.

Configure Magento to purge Varnish