If you do some digging on Zillow.com, you will see they rate their confidence in their estimate by each geographic area.  A rating of five means they are most confident in the value.  A rating of one means they are either using the tax assessed value or “unable to compute Zestimate accuracy”. 



As you'll note above, Harrisonburg scores a ONE by their own admission.  This means that their value estimates are information is totally unreliable.  You can read more about this on Zillow's website.
 
So before you put too much stock in what Zillow might tell you about your home's value --- remember that they themselves would tell you that their value estimates in Harrisonburg and Rockingham County are not at all accurate.