Customer Logout programmatically in Magento 2.

Magento 2, You can log out customer programmatically by getting current customer session using the Model file, Magento\Customer\Model\Session

You need to call logout() function from above class dependency.
Call below dependency in __construct function,

<?php
public function __construct(
    \Magento\Framework\App\Action\Context $context,
    \Magento\Customer\Model\Session $customerSession
) {
    $this->redirect = $context->getRedirect();
    $this->customerSession = $customerSession;
}

public function customerLogout() {
    $customerId = $this->customerSession->getId();
    if($customerId) {
        $this->customerSession->logout()
             ->setBeforeAuthUrl($this->redirect->getRefererUrl())
             ->setLastCustomerId($customerId);
        return "Customer logout successfully";
    } else {
        return "Customer is not login";
    }
}

Call customerLogout() function from above file to programmatically log out a customer from the current session.