The Great Intrusion into creation was sin, which was accompanied by its handmaiden, death (which is both physical and spiritual). It was therefore the work of Christ that had "reconciled" to the Father what sin and death had taken away.
In the epistle to the Ephesians there is a parallel verse that sheds light on the passage in Colossians -
Ephesians 1:9-10 (NASB)
9 He made known to us the mystery of His will, according to His kind intention which He purposed in Him 10 with a view to an administration suitable to the fullness of the times, that is, the summing up of all things in Christ, things in the heavens and things on the earth.
What is in mind here?
It is the disobedience of men and angels, who have established their rule, authority, and power against God on earth. That is, the sinful rule, authority, and power among men and angels have death (which is both physical and spiritual) as its basis, which Jesus "abolished" through the cross (for example, please see 2 Tim 1:10).
Other key verses in this regard are found in Paul's first epistle to the Corinthians -
1 Cor 15:24-26, 28 (NASB)
24 then comes the end, when He hands over the kingdom to the God and Father, when He has abolished all rule and all authority and power. 25 For He must reign until He has put all His enemies under His feet. 26 The last enemy that will be abolished is death. . . 28 When all things are subjected to Him, then the Son Himself also will be subjected to the One who subjected all things to Him, so that God may be all in all.
So the idea here is that there has been all this sin and disobedience among men and angels in creation, and of course this disobedience has thrived within a context of spiritual death -- for example, please compare Eph 2:1-2 with Eph 6:12. Thus we have the Great Intrusion in God's creation, which is now to be annulled through Christ.
This supposition does not mean universal salvation for all sinners, or that God has somehow reconciled the fallen angels to himself; what it means is that Christ has "abolished" all disobedience through his death and resurrection. He removed all sins of all people through his body on the cross. (Please click here for further explication.) However, what is "abolished" at the end of time (as noted in the Corinthian passage above) is death -- that is, those who are spiritually dead (whether men or angels) will perish. Of course, sin is not the issue at the last judgment -- it is instead spiritual death, which is the handmaiden of sin.
While there is no biblical evidence that the death of Christ had anything to do with the sins of fallen angels, his death and resurrection were nevertheless also the basis of the cleansing of "the heavenly things" in Heb 9:23. In other words, the death of Christ not only provided for the atonement of sinners who dwell on the earth, but also included the cleansing of "the heavenly things," which of course were contaminated by sin.
In summary, Christ died to reconcile all things in heaven and on earth contaminated by sin. That is, he "reconciled" all rule, all authority, and all power back to the Father with the sole exception of those spiritually dead (both men and angels), who will burn in eternal fire.