We've been using this API from quite some time. We could see addresses being returned out of the UK & hence changed the geocoding URL to restrict to UK only.
http://maps.googleapis.com/maps/api/geocode/xml?latLng=54,-2&address=gdfgsdgsd,GB
http://maps.googleapis.com/maps/api/geocode/xml?latLng=54,-2&address=gdfgsdgsd,GB&components=country:GB
Please check the results for both of the above URL's. The first URL returns ZERO_RESULTS which is correct. The second one always returns a lat long from centre of UK, no matter what search term we use.
You can also try replacing the value for 'address' to replicate the issue : 452376452334,^$%^$%^$%,458352462354^$%^$%^
Looks like I have found a way to resolve this. The URL pattern I use now is : http://maps.googleapis.com/maps/api/geocode/xml?address=Leeds,UK|GB
The below URL now gives ZERO_RESULTs http://maps.googleapis.com/maps/api/geocode/xml?address=gdfgsdgsd,UK|GB
Also as Joyson suggested, we could also check for the country returned back & display an error message.