config.xml

<?xml version="1.0"?>
<config>
    <!-- ... -->
    <global>
        <models>
            <foobar>
                <class>Foo_Bar_Model</class>
            </foobar>
        </models>
    </global>
    <!-- ... -->
    <adminhtml>
        <events>
            <controller_action_postdispatch_adminhtml_catalog_product_save>
                <observers>
                    <foobar>
                        <class>foobar/observer</class>
                        <method>clearBlockCache</method>
                    </foobar>
                </observers>
            </controller_action_postdispatch_adminhtml_catalog_product_save>
        </events>
    </adminhtml>
    <!-- ... -->
</config>

Dear Grigoriu,
could u please be more specific! Where should the php file goes in and which config.xml file should be modified?

Thanks

By the way, I put your code in a ready-to-use Magento extension two years ago: https://github.com/sprankhub/Spranks_RefreshBlockHtmlCache