No you dont actually need Authentication to clear the cache.If you use authentication you can have better control on your application.
For your application ,
Just add this code to the page load.
Response.Buffer = True
Response.ExpiresAbsolute = Now().Subtract(New TimeSpan(1, 0, 0, 0))
Response.Expires = 0
Response.CacheControl = "no-cache"
What happens is It prevents the page from being cached.so that the page will be loaded as a new page rather than taking values from the cache.