Magento2 – Refresh Cache After an Order is Placed

You could programmatically clear cache within your module using

/**
 * @var \Magento\Framework\App\Cache\Frontend\Pool
 */
protected $_cacheFrontendPool;


public function __construct(
    ....
    \Magento\Framework\App\Cache\Frontend\Pool $cacheFrontendPool,
) {
    ...
    $this->_cacheFrontendPool = $cacheFrontendPool;
}

Then

    /** @var $cacheFrontend \Magento\Framework\Cache\FrontendInterface */
    foreach ($this->_cacheFrontendPool as $cacheFrontend) {
        $cacheFrontend->clean();
    }

See magento2/app/code/Magento/Backend/Controller/Adminhtml/Cache/FlushSystem.php

Finally, I got a solution:

In your custom block, provide a cache tag for your block by assigning cache_tags a unique value for your block.

e.g. in my case, I will set the tag as cache_tags[] = 'custom_skus'

Or you can implement IdentityInterface in your custom block and then override getIdentities method, which will return array of tags.

e.g.

public function getIdentities()
{
    return ['custom_skus_block'];
}

Now, you can observe the save after of admin config and clean the tags using $this->_cacheManager->clean($tags);. Refer here for event of admin config save.

Hope this helps!