HTML:表单和子域

I have a very basic question. Please consider a site with subdomains:

MAIN SITE: www.domain.com

Sub-domain 1: sub1.domain.com

Sub-domain 2: sub2.domain.com

The main site, in http://www.domain.com/index.php, has a form:

<form action="http://sub1.domain.com" method="post">
<input type="text" name="userInput">
<input type="submit">
</form>

Will the data be posted to http://sub1.domain.com and be accessible by the following: (?)

<?php 
  $input = $_POST['input']
  //the goal is to make $input, a variable in http://sub1.domain.com/index.php
  //equal to what the user submitted in the form at http://www.domain.com/index.php
?>

I simply need to load sub1.domain.com/index.php with the posted variables present, no real-time fanciness. From my reading, I've determined there may be a setting which blocks this activity in apache or some other application, but theoretically, data should be able to be sent to any domain/subdomain from any domain/subdomain using POST, correct?

**> Step1: Go to Cpanel select Subdomain icon and click on manage

redirection link of your subdomain. and set redirection to http://sub1.domain.com/xyz.php and save setting

Step 2: Changes in form as below

Step 3: Changed in xyz.php which must be located in inside sub1 directory

sub1 | |__xyz.php

xyx.php file

**