To illustrate the attempts made by the Church of Scotland in the 1640s towards these ends, here is a letter from the General Assembly of the Church of Scotland to the "Kirks in the Netherlands" in the year 1644.
May we recover this vision!
UPDATE 3/4/13: See the comments for a couple of great quotations on this subject from James Porteous in his book, "Jesus Christ the King of the Church." Here is one of them:
Presbytery is the proper manifestation of the unity of the Church. Let these principles of associated representative government be logically and fully embraced, and its range must be commensurate with the entire Church. It cannot stop with nations, it must embrace the world. The visible Church can no more be restricted to nations, or partitioned among these as separate and independent portions, than may the congregations of a locality. The Church is one in all the earth.
UPDATE 5/10/13: The FPCS has recently released a new catechism of its distinctive principles that deals with the subject of the international catholicity of the church.