SQL server service broker usage with ASP.net cache?

Question

I have ASP.net site (4.5) which uses sql cache notification. (using aspnet_regsql.exe)

The idea is that SQL server tables are stored in the app's cache .This is for - not to load data over and over again from the specific table.

The beauty is that Asp.net's cache can automatically remove the table from the cache (and load it again - optionally) when data is modified on that table.

It is done via web.config :

 <system.web>
      <caching>
         <sqlCacheDependency enabled="true">
            <databases>
               <add name="Northwind" connectionStringName="AppConnectionString1" 
                pollTime="500" />
            </databases>
         </sqlCacheDependency>
      </caching>
 </system.web>

But the way it works is by polling the main sql cache Notification table (which basically holds table names and counters)

Question:

I know that service broker can be used instead . But how does the mechanism is different as opposed to polling? I mean - when a table is changed - there is a trigger which updates the main table but how ASP.net knows that a counter (which represent a change) has been increased ? does ASP.net still polls ?