I don't have experience with Pure Lords themselves, but I've researched the inner workings of the Spirit and the power of one's consciousness and may be able to shed some light on how an area where magic does not exist could be created.
From what I've gathered here, and previous discussions I've had regarding Pure Lords, those who can be completely unaffected by magic and create said zones are those with the complete and utterly unshakable belief that Magic itself does not exist. Furthermore, by extending their will outward of themselves, they can create a 'zone' in which that belief holds true. Be aware, though it may have similar effects to a suppression, it is fundamentally different: a suppression works under the logical bounds of magic, that something of finite power can be restrained by a greater power, and thus has the logically equivalent weakness of being broken should a power greater than that suppressing the original power be enacted upon it.
The power of a Pure Lord with the ability to manifest his will outside himself follows no such logic, as their power itself is not derived from logic, nor from magic: put simply, within the confines of that barrier, for all intents and purposes, magic does not exist. Any attempts to use magic will bear no fruit, even dragon magic. As to that zone's 'weakness', it thrives off the Pure Lord's absolute will, which means that should his will disappear, so will that zone. Given that, you are left with four ways to eliminate the zone: kill him, convince him to take it down, make his belief that magic does not exist waver, or, theoretically, find a person with an absolute belief in magic to enter that zone. Given that the third option would be almost completely fruitless, I would suggest you try the second option. This will most likely prove difficult, seeing as he believes magic does not exist, and therefore will not easily understand your plight. Killing him is also possible, as it was said previously in this discussion, they are not immortal, however, you will certainly need substantial force to do so.
The fourth option is probably the trickiest: essentially, it would be finding some being whose very existence is based around the existence of magic. I have never met such a being, but if you could find one, they could theoretically break the zone. This is because they, themselves, would exist separate of magic inside that zone, but because they exist inside that zone, magic would also have to exist by their absolute belief in it: thus, they would create a paradoxical relationship between their will and the will of the Pure Lord, causing both effects to cancel, breaking that zone.
I hope some of this will aid you in your endeavor.
- Wycliff, the Seeker of Spirit.