Country Code Top Level Domains or ccTLDs represent a specific country and websites with .com.au would indicate that this website contained content for Australia while a .co.uk site would contain content for the UK. If you require such specific domains then you will need to prove that your website is operating in that specific country.
While such registrations were restricted in the past, currently most countries allow anyone to register. On the other hand, domains like .com are generic in nature. Google’s search engine algorithms factor in site location during ranking and a person searching in Australia will probably get to view .com.au sites higher in the results. However, Google also considers several other factors including server location to determine the relevancy of a website to a particular query.
Website owners using Google Webmaster Tools have the ability to specify a target country for generic TLDs, but not for country-specific TLDs that are restricted to a particular country. Still, this limited feature in the past had disappointed several web owners that desired a global presence while being registered in a particular country. Certain web owners in countries such as Colombia that had the ccTLD of .co, wanted to rank in searches outside their country, but were unable to do so in the past.
However, Google has now expanded their generic TLD list that includes several ccTLDs. You now have the ability to specify any specific country that you wish your site to be associated in search results.
If you do not want your site to be related to any country then you should not specify any country. This will indicate to Google bots that your unrestricted ccTLD should not be associated with any specific country and will in turn provide appropriate rankings for related searches.