if ( empty ($domain1) && ( empty ($domain2))
{ 
	echo 'both are empty';

elseif ( empty ($domain1) && ( !empty ($domain2))
{
	echo 'domain1 is empty, domain2 is not';
} 

elseif ( !empty ($domain1) && ( empty ($domain2))
{
	echo 'domain1 is empty, domain2 is not';
}