Angular clear subform data and reset validation

Set the name attribute on the subform and then you can $scope.formName.$setPristine(); where formName is what the name attribute is. An element is no longer pristine when the value has been changed.

http://docs.angularjs.org/api/ng.directive:form.FormController#$setPristine

Update
The above answer was solely for 1.2, but in 1.3 angular introduced the concept of a "touched" input. Now when an element is blurred angular will mark the field as touched. Similar to $setPristine, you can set the input back by using $scope.formName.$setUntouched().

https://docs.angularjs.org/api/ng/type/form.FormController#$setUntouched

touched vs pristine: touched means the field has been blurred while pristine means the field's value has been modified. Angular's docs note that "Setting a form controls back to their untouched state is often useful when setting the form back to its pristine state."

Edit
Here is a fiddle demo: https://jsfiddle.net/TheSharpieOne/a30kdtmo/

angular.module('myApp', [])
  .controller('myCtrl', myCtrl);

function myCtrl() {
  var vm = this;
  vm.reset = function() {
    vm.myForm.$setPristine();
    vm.myForm.$setUntouched();
    vm.email = vm.password = '';
  }
}
.ng-invalid.ng-touched {
  outline: 2px solid blue;
}
.ng-invalid.ng-dirty {
  outline: 2px solid red;
}
.ng-invalid.ng-dirty.ng-untouched {
  outline: 2px solid green;
}
form,
form div {
  padding: 5px 10px;
}
h3,
h4 {
  margin-bottom: 0;
}
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.0/angular.min.js"></script>
<div ng-app="myApp" ng-controller="myCtrl as ctrl">
  <form name="ctrl.myForm">
    <div>
      <label for="email">Email</label>
      <input name="myInput" type="email" ng-model="ctrl.email" id="email" required>
    </div>
    <div>
      <label for="password">Password</label>
      <input name="myPassword" type="password" minlength="8" ng-model="ctrl.password" id="password" required>
    </div>
    <div>
      <button ng-click="ctrl.reset()" type="button">Reset</button>
    </div>
  </form>
  <div>
    <h4>Form Level</h4>
    <div>$dirty: {{ctrl.myForm.$dirty}}</div>
    <div>$pristine: {{ctrl.myForm.$pristine}}</div>
    <h4>Input Level</h4>
    <h5>Email Input</h5>
    <div>$dirty: {{ctrl.myForm.myInput.$dirty}}</div>
    <div>$pristine: {{ctrl.myForm.myInput.$pristine}}</div>
    <div>$touched: {{ctrl.myForm.myInput.$touched}}</div>
    <h5>Password Input</h5>
    <div>$dirty: {{ctrl.myForm.myPassword.$dirty}}</div>
    <div>$pristine: {{ctrl.myForm.myPassword.$pristine}}</div>
    <div>$touched: {{ctrl.myForm.myPassword.$touched}}</div>
  </div>
  <div>
    <h3>Color outlines for input</h3>
    <div title="The form loads this way, it can still be invalid since required fields are empty to start with">untouched, pristine: no outline</div>
    <div title="Such as in the middle of typing a valid email for the first time">invalid, untouched, dirty: green outline</div>
    <div title="blurred with invalid input">invalid, touched, dirty: red outline</div>
    <div title="focued and blurred without typing">invalid, touched: blue outline</div>
  </div>
</div>