Several ongoing research efforts aim to design potential Future Internet Architectures, among which Named-Data Networking (NDN) introduces a shift from the existing host-centric Internet Protocol-based Internet infrastructure towards a content-oriented one. However, researchers have identified some design limitations in NDN, among which some enable to build up a new type of Distributed Denial of Service attack, better known as Interest Flooding Attack (IFA). In IFA, an adversary issues not satisfiable requests in the network to saturate the Pending Interest Table (PIT) of NDN routers and prevent them from properly handling the legitimate traffic. Researchers have been trying to mitigate this problem by proposing several detection and reaction mechanisms, but all the mechanisms proposed so far are not highly effective and, on the contrary, heavily damage the legitimate traffic. In this paper, we propose a novel mechanism for IFA detection and mitigation, aimed at decreasing the memory consumption of the PIT by effectively reducing the malicious traffic that passes through each NDN router. In particular, our protocol exploits an effective management strategy on the PIT, through which the Malicious Interest (MIs) already stored in the PIT are removed and the new incoming MIs are dropped. In addition, the proposed countermeasure provides an additional security wall on the edges of the network to detect and mitigate the attack as early as possible and improve the network health, i.e., routers PIT occupancy during IFA. To evaluate the effectiveness of our work, we implemented the proposed countermeasure on the open-source ndnSIM simulator and compared its effectiveness with the state of the art. The results show that our proposed countermeasure effectively reduces the IFA damages both in terms of preserved legitimate traffic and availability of routers PIT. Considering the legitimate traffic, the amount of Benign Interests preserved by our approach increases from 5% to 40% with respect to the preservation guaranteed by the state-of-the-art solutions. Concerning the routers PIT availability, our approach guarantees that the 97% of the PIT size is left free for handling the legitimate traffic.