U.S. money managers are reversing a decade-long trend of diversifying away from the dollar, leading more strategists to conclude that a rally that's taken the currency to a four-year high is just getting started.

Investors based in the U.S. hold 19.3 percent of their $35.8 trillion of equities in foreign shares, down from a peak of 21.1 percent in 2009, according to new Federal Reserve data tracked through June by UBS AG. After surging from 8.3 percent in 2003, the proportion of their $11.4 billion of bonds, excluding Treasuries, that is in foreign debt has stabilized at 20.9 percent.

"This, and the fact that relative growth is better in the U.S. and the currency is still cheap, means the dollar will rise further," Geoffrey Yu, a senior currency strategist at UBS in London, said by phone on Oct. 16.