Use TYPO3 cache tags in a plugin

DummyController.php

<?php
namespace In2code\Contacts\Controller;

use TYPO3\CMS\Extbase\Mvc\Controller\ActionController;

/**
 * Class ContactController
 */
class ContactController extends ActionController
{

    /**
     * @return void
     */
    public function contactAction()
    {
        $this->view->assign('contact', ['uid' => 123]);
        $GLOBALS['TSFE']->addCacheTags(['contact']);
    }
}

PageTSconfig.typoscript

# clear all pages with plugin contact if there is a change in PID 2529 or in children pages
[PIDinRootline = 2529]
TCEMAIN.clearCacheCmd = cacheTag:contact
[end]