Hi Anurag,
What you'll likely want to do in this scenario is leverage the Referrer constraint of the Visited Web Page trigger/filter. You'll want to create a smart list for each domain you want to track like this:
Visited Web Page is Your Landing Page
Add Constraint
Refferer contains example.com
This will pick up anyone who visited that page coming in from the example.com domain.
For the New Names, this is a bit trickier, and you'll probably want to submit a hidden form field with lead source for new leads. You could do this with individual landing pages, but a little script can let you do it dynamically with one page:
MktoForms2.whenReady( function (form) {
if (location.host.search("example.com")){
form.vals({"Lead Source":"example.com"});//you can change example.com to whatever value you want to use
}
else if (location.host.search("marketo.com")){
form.vals({"Lead Source":"marketo.com"});
}
//add more repetitions here if necessary
});