In a nutshell, Article 54 of the New York CPLR sets forth the procedure to simply register a judgment entered in another state.
So long as the foreign court had jurisdiction to enter that judgment, it will be entitled to "full faith and credit" under the United States Constitution. New York will honor it.
Although out-of-state judgments obtained by default are entitled to full faith and credit, they may not be simply registered under Article 54. Rather the creditor must seek to have the judgment recognized through a "plenary action" (full notice with opportunity for trial) or through a Motion for Summary Judgment in Lieu of a Complaint under CPLR § 3123.
At The Langel Firm, the bulk of our clients are battling default judgments largely due to outdated addresses leading to improper service. This problem is not limited to New York but becomes New York's problem when the debtor needs to defend against its enforcement here.
Article 54 reminds us that additional precautions apply to all default judgments.
If any creditor is seeking to enforce a sister-state judgment against you, we would be delighted to help you explore your legal defenses.
 Article IV, § 1 of the United States Constitution requires all states to afford full faith and credit to judicial proceedings of other states. 28 U.S.C.A. § 1738 extends full faith and credit to the proceedings and judgments of any territory or possession of the United States (including the District of Columbia).