What Aquinasfan doesn't seem to realize is the fact that while there is the invisible church, there are also local gatherings of believers who constitute the local church.
Now, in churches with an established heirarchy, the "local" in "local church" may be greatly extended, all the way up to the top. This is one of the reasons that I think that we Baptists have it right when we insist on local church autonomy. For example, the SBC doesn't tell any Baptist church what to do. The SBC exists for the churches, not the churches for the SBC. This is a difficult concept for non-Baptists to grasp. In fact, the SBC only exists for a couple of days each year, when the Convention meets for business. There are organizations that exist under the SBC umbrella, such as our Seminaries, publishing house, missions boards, etc., but they technically are not the SBC.
Now, on to the question at hand.
If there is a need for church discipline within a local church, the local Baptist church will carry out the requirements of Matthew 18, and they don't have to answer to anyone other than Christ. I have seen several instances where members were "disfellowshipped" under Matthew 18, and it is never pretty, but it is required.
As far as disciplining Christians who do not belong to your local church, that is a matter for the local congregation to which they belong.
However, let's pose a theoretical case: Suppose that Uriel1975, an orthodox Presbyterian, was to cheat me in business, and that I was to consider him to be a Christian brother and not a "tare". (I know that he would never cheat anyone, much less me, but I also know that he will undestand my point). My first step would be to go to him in private, and attempt to reason with him and obtain relief. If he was to rebuff me, then I would contact the Pastor or another elder in his local church, and take them with me to talk with him. If he was to continue to resist, then I would expect the leadership of his local congregation to take appropriate action in "disfellowshipping" him.
And what if they don't? Where can you go to appeal or settle the matter?
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Another problem. If "the church is the pillar and foundation of truth," then how can it be possible for two churches to teach conflicting doctrines, especially doctrines regarding salvation? How can their be "two truths"?