PHP- Domains validation separated by comma

PHP- Domains validation separated by comma

How can i validate domains separated by comma, like
site.com,site2.com,sub.site3.com which are coming from a textarea return
true or alse in PHP. thanks
if($_POST['domains'] != '')
{
//validation here
}
else
{
$check ="1";
echo "Error, You didnt enter a domain name!";
}