A network engineer has configured a single-hub DMVPN with two spokes. Spoke-to-spoke tunnels form correctly, but the engineer notices that after a spoke reboots, its dynamic NHRP mapping remains on the hub for far longer than expected, causing the hub to attempt forwarding traffic to an unreachable spoke before purging the entry. On the hub tunnel interface, the current configuration includes 'ip nhrp holdtime 7200'. Which action best resolves the delayed purging of stale spoke registrations?