How does the cache work in Magento2?

I have found more info and directly linked with data changes (index therefore). The cache in Magento is built with tags.

I will describe an example below that may show the product category listing can reflect the latest products' data without incurring huge costs on the server activity.

Many blocks in Magento 2 do implement the interface MagentoFrameworkDataObjectIdentityInterface.

I invite you to take a look at these 3 functions:

MagentoCatalogModelCategory::getIdentities
MagentoCatalogBlockProductListProduct::getIdentities
MagentoCatalogModelProduct::getIdentities

Particularly, the second function for the ListProduct Block is very interesting as you can see we are crawling the product collection and check the products 'identities' like a recursive mechanism..

Now, to understand deeply this tag power, it may require practice, I do invite you to create your own tag and then create a block that has data for this tag.. Tags are also visible in the backend (System/Cache Management) so you should see your tag in the backend once created. Then you can add your custom index but we may accept this may be out of scope here.

we can still learn a lot about cache in Magento looking at: https://github.com/mage2tv/magento-cache-clean. Vinai has spent a fair amount of time on this I believe. . If you have time and want to thoroughly understand the cache, this will help you more than likely.