The Swiss franc shock reverberated through currency trading firms around the world on Friday, wiping out many small-scale investors and the brokerages that cater to them and forcing regulators to take a closer look at the sector. Some major banks also lost out when the Swiss National Bank scrapped its three-year-old cap on the franc against the euro (EURCHF=EBS) without warning on Thursday, including Britain’s Barclays (BARC.L) which lost “tens of millions” of dollars, an industry source said.